"We need to pay physicians and hospitals in ways that reward them for eliminating early elective deliveries, reducing unnecessary C-sections and preventing complications of childbirth," said Suzanne Delbanco of Catalyst for Payment Reform, a nonprofit employer coalition, in a statement.

Truven estimated that U.S. spending on maternity care would drop by more than $5 billion if only 15 percent of pregnant women chose C-sections — the rate recommended by the World Health Organization — compared with the current 33 percent.

The number of C-sections has risen by half over the last decade for a variety of reasons.

Monday's study was also sponsored by Childbirth Connection, a nonprofit group that provides information about maternity care, and the Center for Healthcare Quality and Payment Reform.

—This post was last changed Wednesday at 5:25 p.m. to reflect that many factors contribute to the rising prevalence of U.S. C-sections.